The Science Journal of the American Association for Respiratory Care

1997 OPEN FORUM Abstracts

ULTRASONIC NEBULIZATION WITH A CONTEMPORARY FLOW-TRIGGERED VENTILATOR.

Michael McPeck BS RRT, Deniese S. LeBlanc BS RRT, Gerald C. Smaldone MD PhD. Departments of Respiratory Care and Medicine. University Medical Center, State University of New York at Stony Brook.

BACKGROUND: Prior to the advent of contemporary ventilators, delivery of aerosolized drugs during mechanical ventilation was relatively easy and the results were predictable. Using pneumatic nebulizers, driven by pneumatic circuits within the ventilator, our group previously found that aerosol delivery was generally similar among 3 popular brands of ventilator, and inhaled mass during a typical adult breathing pattern ranged from 9.6 to 14.7% (mean ±SD - 13.0%±1.8%) while treatment time averaged 30 min (McPeck, et al. Respir Care 1993;38:887-895). Some contemporary ventilators now depend on a constant bias flow in the ventilator circuit and upon "flow triggering" rather than pressure triggering to detect the beginning of a patient-initiated breath. However, flow introduced through a pneumatic nebulizer disables the flow triggering capability of the ventilator and interferes with the accurate measurement of exhaled volume. The Siemens Ultrasonic Nebulizer 345 (SUN) was developed to obviate this problem during mechanical ventilation with the Siemens Servoventilator 300 (SSV300). We designed this study to determine whether the SUN provides aerosol delivery equivalent to conventional pneumatic nebulizers. Methods: Using a test bench protocol incorporating an SSV300, an ETT and a test lung, we measured the quantity of aerosol generated by 3 different SUNs charged with 3.0 mL of technetium (^{99m}Tc) radiolabeled unit dose albuterol solution. A low-resistance absolute filter was used to collect the radioaerosol delivered to the distal tip of the ETT, the quantity of which was expressed as a percentage of the nebulizer charge (inhaled mass %). A preliminary experiment confirmed that ^{99m}Tc behaved identically to albuterol in the SUN. Serial measurements over time of filter radioactivity were made with each nebulizer until cumulative radioactivity reached a plateau corresponding to the end of nebulization ("dryness").

(See original for figure)

Results: Aerosol delivered to the ETT filter varied from 19.7 to 26.2% inhaled mass (Figure) with a mean ±SD of 23.0 ±2.6%. Each of the SUN units reached the plateau in 8 minutes. We did not observe interference with ventilator function during operation of the SUN.

CONCLUSION: The SUN 345 exceeded the performance of typical pneumatic nebulizers from our previous study when used under similar conditions with the SSV300 ventilator and an adult breathing pattern. Aerosol delivery averaged 1.8 times greater (23.0% vs. 13.0%) while treatment time was reduced by a factor of 3.8 times (8 min vs. 30 min). In addition to improved aerosol delivery, we regard the absence of interference with flow triggering and monitoring as clinically significant.

OF-97-066

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